As is well known and by way of background, natural gas is a naturally occurring hydrocarbon gas mixture consisting primarily of methane, up to 20% other hydrocarbons as well as varying amounts of impurities such as carbon dioxide. Natural gas is widely used as an energy source and it is generally found in deep underground natural rock formations or associated with other hydrocarbon reservoirs. The underground rock formations or subsurface reservoirs of hydrocarbons typically consist of a porous layer, such as limestone and sand, overlaid by a nonporous layer. The porous layer forms a reservoir in which hydrocarbons are able to collect. To recover hydrocarbons, wells are drilled from the surface of the earth through the nonporous layers overlying the reservoir to tap into the reservoir and allow the hydrocarbons to flow from the porous formation into the well. The hydrocarbons, including oil and natural gas, are then recovered at the earth's surface where they undergo further processing.
Recovering natural gas is often not as straightforward as it appears, as the gas may not readily flow from the reservoir into the well bore as a result of a variety of factors including formation characteristics and pressures. As such, as is well known in order to increase gas flow and recovery, many methods are employed as means of increasing natural gas production including horizontal drilling and hydraulic fracturing, or “fracing”. Horizontal drilling, as opposed to vertical drilling, involves drilling a well more or less horizontally through a reservoir to increase the exposure of the formation to the wellbore, thereby decreasing the distance the gas must travel to the wellbore.
Hydraulic fracturing involves pumping high pressure fluids and sand into the reservoir in order to open up the formation by fracturing the rock in the reservoir. After the pressure is released, the sand remains in the fracture to create a higher permeability flow path towards the well.
Horizontal drilling and hydraulic fracturing are generally effective at increasing the recovery of hydrocarbons, however they also create additional challenges that must be dealt with. Specifically, large quantities of fluid, sand and other additives are introduced into the formation and mixed with the hydrocarbons during fracturing. After the fracing stimulation of the well, introduced fracing sand and naturally occurring reservoir fines or sand and/or fracing sands can be produced back into the horizontal well along with any remaining fluids, natural gas and other reservoir fluids. This particulate is produced to the surface and can cause plugging and/or erosion of surface equipment and pipelines.
To remove sand from natural gas at the surface, apparatuses commonly referred to as sand separators are used. Typically a sand separator comprises a vessel with an inlet port and a gas outlet port on the upper part of the vessel, and a drain at the bottom of the vessel. In addition, this vessel may or may not include secondary filters. The inside of the vessel is formatted such that when a high pressure, high velocity production stream from a well flows into the vessel through the inlet port, it experiences a large drop in velocity, causing the natural gas to separate from the water and sand. The vertical divider forces the fluid and sand down towards the drain, while the gas rises back up around the divider and exits through the gas outlet port.
While past sand separators can be effective, they are often limited by a number of operational limitations in the field. For example, the flow rate of gas and water/sand into a sand separator may be varied where the velocity of gas and the volume of water/sand may fluctuate significantly as it enters the sand separator. In particular, in the event that a sudden pulse in water/sand is encountered, in past designs, this may lead to either ineffective water/sand separation from the gas, clogging of the sand filters of the separator and/or damage to the sand filters. An example of a past sand separator is described in U.S. Pat. No. 7,785,400. As a result, there has been a need for systems that effectively allow for a greater residence time of water/sand within the separator that enables a more efficient separation of water/sand from gas without leading to clogging problems.